DANE, WI - MARCH 24: With his wife Heidi by his side, Republican presidential candidate Sen. Ted Cruz (R-TX) tours the Dane Manufacturing facility before speaking to workers on March 24, 2016 in Dane, Wisconsin. Wisconsin voters go to the polls for the state's primary on April 5. (Photo by Scott Olson/Getty Images)

Ted Cruz has launched one of the angriest and most stinging attacks of the 2016 presidential campaign, labelling opponent Donald Trump "a snivelling coward" after attacks on Cruz's wife.

The Republican presidential campaign has taken an especially nasty turn in recent days, after Trump claimed he would "spill the beans on [Cruz's] wife," Heidi. Trump was responding to an ad produced by an anti-Trump group called Make America Awesome, which shows Trump's wife Melania posing for a GQ Magazine photoshoot in 2000. The images of Melania Trump have since been used in pro-Cruz, anti-Trump online memes, but CNN reports the Make America Awesome group "has no known connection to the Cruz campaign."